This invention pertains generally to skyline logging systems and specifically, to such systems incorporating a skidding line, carriage and hoisting line.
In a conventional gravity skyline yarding system, the skyline is suspended between a mast or spar pole located adjacent a log-landing area and a tailhold which is typically a tree stump located down a slope from the landing area. Tension in the skyline is provided by a yarder, located at the landing. A carriage is mounted for reversible travel on the skyline. Transportation down the skyline is provided by gravity while transport up is provided by a skidding line also connected to a powered winch drum on the yarder. The skidding line passes from the yarder over a sheave or pulley mounted on the mast. From there it extends and is attached to a hoisting line. This latter line extends through the carriage over a swivel fairlead down toward the ground. The hanging end is fitted with a loop or clip for receiving choker cables used for hauling logs from the slope.
The carriage typically has a radio-controlled clamp on both the skyline and the hoisting line. During initiation of a logging operation in which the yearder is higher on a slope than the tailhold, the carriage is placed on the skyline near the yarder with both line clamps closed. The skyline clamp is released, allowing the yarder gradually to let the carriage slide down the skyline by paying out the skidding line. When the carriage reaches the desired location it is stopped by braking of the skidding line drum, the skyline clamp is closed and the hoisting line clamp is opened. By continuing to payout the skidding line from the drum and by inhauling the winch line in the carriage, the hoisting line is allowed to feed through the carriage as the suspended end drops to the ground under the pull of gravity. This letting out of the hoisting line is not practical because the skidding line tends to sag between the mast and carriage. This sagging causes the skidding line to defeat the pull of gravity caused by the suspended end of the hoisting line. However, by proper feeding by the yarder and inhauling the winch line in the carriage, the gravitational forces acting on the hoisting line win out.
The hoisting line is then secured to a log which has been cut and readied for removal from the forest. The yarder then reels in the skidding line which in turn causes the hoisting line, moving through the carriage, to lift the log toward the carriage. When the log achieves a desired height above the ground, the hoisting line clamp is closed and the skyline clamp is opened. By continued reeling in of the skidding line, the carriage and the accompanying suspended log are pulled to the yarding area. At this point the skyline clamp is closed and the hoisting line clamp released. By paying out the skidding line and inhauling the winch line in the carriage, the load is lowered to the ground.
Although this description has referred specifically to a gravity system, it will be appreciated that it can be used in other applications as well.
Various systems exist which provide means for hoisting logs to a carriage. One type uses a separate cable which is driven by the yarder to pull the logs up. Another type uses a carriage-mounted engine to haul the line onto a carriage-mounted drum or reel. None of these, however, assist gravitational forces in feeding out a hoisting line from the carriage.
It is, therefore, a general object of the invention to provide a skyline logging system which exhibits increased operational speed.
It is more specifically an object to provide in a carriage power-driven means for assisting gravitational forces in lowering a hoisting line attached to a skidding line.